We note that \(B_{20}\)  arises due to other shaping components of the surface [1]}. In axisymmetry, negative values of \(B_{2c}\)  contribute to positive (outward-pointing) triangularity (\(X_{2c}<0\) ) ((B11) in [2]}). Assuming stellarator symmetry, negative values of \(B_{2c}\)  contribute to positive values of \(B_{20}\)  if the surface is vertically elongated, and positive values of \(B_{2c}\)  contribute to positive values of \(B_{20}\)  if the surface is horizontally elongated. This implies that positive triangularity coupled with vertical elongation or negative triangularity coupled with horizontal elongation contributes to the magnetic well in axisymmetry. These trends are consistent with the stability analysis of oblate plasmas with negative triangularity [3]}, [4]}, [5]}. In 3D, the connection between \(B_{20}\)  and \(B_{2c}\)  is more complicated ((A41)-(A42) in [1]}). Nonetheless, we note that the magnetic well near the axis arises at second order in the expansion parameter, which includes the effects of ellipticity and triangularity. Thus it is not surprising that the optimized boundary with curvature constraints features rotating ellipticity and triangularity.
